The wife of a prison officer killed in a motorway ambush in Northern Ireland has called for no retaliation over his murder.

David Black - who had spent more than 30 years in the prison service and was approaching retirement - was gunned down in an attack believed to have been carried out by dissident republicans in Northern Ireland.

The father-of-two's wife Yvonne has appealed for no retaliation for the killing, which has been condemned by politicians on all sides.

She said in a statement: "Grief and sadness in another home will achieve nothing."

Mr Black, 52, was shot on Northern Ireland's M1 motorway early in the morning as he drove to the top security Maghaberry jail near Lisburn, County Antrim.

The attack happened at the M1/M12 turnoff in County Armagh

Police said the gunman was in a Toyota Camry with a Dublin registration which drew alongside Mr Black's black Audi.

Shots were apparently fired at Mr Black from the vehicle, causing his car to veer off the road and into a drainage ditch.

At the time bomb disposal experts were attending a security alert further along the motorway, which police believe may have been set up as a decoy.

Police attending the scene

No organisation has admitted responsibility, but security chiefs believe republicans opposed to the peace process were involved.

The extremists have been involved in long-running protests against jail conditions inside Maghaberry.

Prime Minister David Cameron said the shooting would not derail the peace process in Northern Ireland.

He said: "This is a dreadful tragedy for the family and friends of David Black who has been so brutally murdered as he went about his work keeping the people of Northern Ireland safe.

"These killers will not succeed in denying the people of Northern Ireland the peaceful, shared future they so desperately want."

The motorway was closed following the shooting

Police Service of Northern Ireland (PSNI) Chief Constable Matt Baggott said: "It was a completely senseless attack. It demonstrated the recklessness and ruthlessness and sheer dangerousness of those who oppose peace and are dedicated to taking us back to those dark days of the past.

"This has all the hallmarks of dissident republicans. This was just a brutal attack and we need the public's support to be able to solve it as quickly as possible."

It is 18 months since renegade republicans claimed the life of police officer Ronan Kerr in Omagh, County Tyrone.

Mr Black had expressed interest in early retirement but no date had been set, Prison Service director general Sue McAllister said.

"We will not allow this to derail the efforts that we are making to reform the service but we will do everything we can to support all of our staff in the very difficult days ahead," she added.

Theresa Villiers said the murder was "cowardly and evil"

A car used in the attack was later found burnt-out in Lurgan, Co Armagh, where supporters of dissidents have backed the jail protest campaign.

It is understood his service stretched back as far as the 1981 IRA hunger strike inside the Maze prison, when 10 republicans starved themselves to death.

Finlay Spratt, the head of the Prison Officers' Association, who knew Mr Black and described him as "a very nice fellow to work with", criticised the security provisions offered to prison officers since the Troubles ended.

"They have stripped away all the security around prison officers," he said.

Stormont First Minister Peter Robinson and Deputy First Minister Martin McGuinness both condemned the murder.

"At this time, our thoughts and prayers are with the bereaved family and we condemn this murder in the strongest possible terms," they said in a joint statement.

The shooting happened at around 7.30am, at the same time as a major security alert further along the motorway at a shopping centre at Sprucefield, near Lisburn, where bomb disposal experts were called in to check a car.

It is believed this vehicle might have been linked to the shooting,

Only a day ago, Northern Ireland Secretary Theresa Villiers warned that the threat from dissident republicans in Northern Ireland remained severe. She described the latest attack as "cowardly and evil".

The Republic of Ireland's foreign minister Eamon Gilmore also expressed his condolences.

"I know that I speak for every decent man, woman and child on this island, North and South, in expressing revulsion at this act," he said.